1. Field of the Invention
This invention relates to a golf ball providing an increased carry. It also relates to a master model and a mold for use in the molding of such golf balls.
2. Prior Art
Golf balls are conventionally manufactured by molding. Normally a plurality of dimples are formed in golf balls for improving aerodynamics thereof. Then the golf ball-forming mold on the cavity surface thereof must be provided with a plurality of protrusions corresponding to the dimples.
Such a golf ball mold is often prepared by reversing a master model having recesses corresponding to the protrusions. The master model having recesses, in turn, is typically prepared by a method as shown in FIG. 7. There are furnished a metallic master block of hemispherical shape 11 and a cutter 12. While the cutter 12 is rotated about its axis, the cutter 12 is fed into the hemispherical surface of the master block 11 to a certain depth from a reference position, thereby machining a recess in the master block 11. With a fixed quantity of feed, recesses (or dimples) of the same diameter and depth are machined. Japanese Patent Application Kokai (JP-A) No. 55364/1994 discloses a method for forming recesses by electric discharge machining instead of a cutter.
When it is desired to provide a master model with plural types of recesses (dimples) having different diameter, depth and/or cross-sectional shape, the above-mentioned prior art methods for forming master models must use plural types of cutters. Cutters must be replaced many times before all types of recesses are formed. The frequent cutter replacement is cumbersome and adds to the cost. There is a demand for improvement in this respect.
For golf balls, there is always a demand for improving the aerodynamics, especially distance.